1. Field of the Invention
The present invention relates to a solid electrolytic capacitor, the solid electrolytic capacitor comprising an anode of valve metals or of an alloy of which main component is valve metals, a dielectric layer formed by anodizing said anode, an electrolyte layer formed on said dielectric layer, and a cathode formed on said electrolyte layer. Particularly, the invention relates to a solid electrolytic capacitor wherein a silver layer using silver is formed for said cathode.
2. Description of the Related Art
In recent years, solid electrolytic capacitors have been widely used for a variety of electronic equipments.
Generally, it has been known such a solid electrolytic capacitor fabricated by: anodizing an anode of valve metals, such as tantalum, aluminum, niobium and titanium, or of an alloy thereof to form a dielectric layer of the oxide on the anode surface; overlaying an electrolyte layer using a conductive polymer or manganese dioxide and the like on the dielectric layer; and overlaying a carbon layer using a carbon and a silver layer using silver as a cathode on the electrolyte layer. (See, for example, Japanese Published Unexamined Patent Application No. 3-46215.)
However, a problem of the above-described solid electrolytic capacitor has been that, particularly, under a high temperature and high humidity environment, silver contained in the silver layer of the cathode is dissolved and ionized, causing migration of silver of re-deposit of silver on the anode surface, which results in occurrence of short circuit and increase of leakage current.
Therefore, in recent years, it has been proposed to prevent migration of silver contained in a silver layer by adding boron simplex powder or boron intermetallic compound powder to the silver layer. (See, for example, Japanese Published Unexamined Patent Application No. 6-151261.)
Nevertheless, the above-described solid electrolytic capacitor still has a problem that it is impossible to fully prevent migration of silver contained in the silver layer even in the case of adding boron simplex powder or boron intermetallic compound powder to the silver layer, therefore, it still causes occurrence of short circuit and increase of leakage current under a high temperature and high humidity environment.